Along with the recent development of wireless communication technology, wireless communication has been extended its application from human communication to device-to-device communication or the Internet of things. Accordingly, it is expected that all things around us will be interconnected through a wireless communication network and controlled wirelessly in the near future.
If such an era is defined as a networked society, the requirements of a wireless network design for building the networked society may include device-to-device communication without human intervention, ultra-connectivity that may reduce a latency between devices, and ultra-short latency/high-reliability transmission between devices.
Device-to-device communication or the Internet of things may find its applications in a variety of fields around us. Particularly, it may be used for building an Intelligent Transport System (ITS) being one of services available through convergence between a wireless communication technology and a vehicle as well as in industry automation or autonomous vehicles.
The services available through convergence between a wireless communication technology and a vehicle may include self-driving of vehicles, provisioning of high-reliability real-time traffic information, and provisioning of a high-quality wireless communication environment to a passenger in a vehicle.
Conditions required to realize such a service through convergence between a wireless communication technology and a vehicle vary depending on the property of the provided service. In regard to a wireless communication-based vehicle safety service, if the requirements of accurate recognition and instantaneous indication of an emergency situation are considered for the service, a wireless communication technology that enables ultra-short latency and high-reliability transmission should be applied. If a high-quality wireless communication environment is to be provided to a vehicle passenger, a wireless communication technology that maintains a uniform channel quality in any situation is preferably applied.
More specifically, the wireless communication-based vehicle safety service may refer to a service in which when it is determined that a vehicle is likely to face emergency due to an external or internal factor or a device of a vehicle is abnormal, the emergency or the abnormal state of the device is notified to a vehicle user through an in-vehicle communication network so that the vehicle user may efficiently handle the problem.
The in-vehicle communication network may be divided largely into a vehicle internal network and a vehicle external network. A vehicle internal network called In Vehicle Network (IVN) is a wireless/wired communication network between sensors, electronic devices, or devices inside a vehicle. The IVN is a technology used to notify a vehicle user of an emergency situation or an abnormal part of the vehicle, as described above.
Besides the IVN technology, the vehicle communication network may also include a vehicle external network, that is, an out-vehicle network from the perspective of a vehicle.
The vehicle safety service using the foregoing IVN is provided to a driver by a specific indication through an audio, a gauge, or the like in a vehicle. However, this information is perceivable only to the driver of the vehicle.
Since the driver of a following vehicle or a nearby vehicle has no way to perceive the above information, the following vehicle or the nearby vehicle may cause an accident to the vehicle, or the vehicles together may be subject to a secondary accident even though the driver of the vehicle takes an appropriate action with the vehicle safety service based on the IVN.
To overcome the problem, a vehicle safety service using a vehicle external network as well as the vehicle safety service using an IVN is continuously studied.
That is, the vehicle safety service using a vehicle external network has been introduced to provide a vehicle safety service using a vehicle communication network technology in relation to other nearby vehicles. Vehicle external networks may be classified largely into Vehicle to Infrastructure (V2I) and Vehicle to Vehicle (V2V).
V2I refers to communication infrastructure between a vehicle and its adjacent Base Station (BS), and V2V refers to communication infrastructure between a vehicle and another vehicle.
If V2I is used, a vehicle may receive traffic information from an adjacent BS, and transmit location information about the vehicle or emergency information sensed by the vehicle to the adjacent BS. The BS and other vehicles share the emergency situation through the transmitted information.
If V2V is used, a vehicle may receive traffic information from a nearby vehicle and may also exchange emergency information sensed by each vehicle.
The foregoing vehicle safety services using a vehicle external network, V2I and V2V may be used mainly for the purpose of sharing information between a vehicle and another object. However, to transmit information to be shared, initial access is performed at each communication. Thus, a long latency is incurred by the initial access.
Accordingly, there is a need for a method for reducing a latency incurred by the initial access. Thus, it is necessary to generate a signal for short latency in a wireless communication system.